Cleaner Bus Emissions

Since 1993, the California Air Resources Board (ARB) has been implementing a strategy for reducing emissions from diesel-powered urban transit buses. Beginning in 1993, the ARB has set increasingly more stringent emission standards for diesel-fueled vehicles and engines sold in California, including buses and their replacement engines. At its February 24 meeting, the ARB proposes to further reduce emissions from urban bus fleets by adopting a rule that will give the transit agencies the flexibility of a choice between two paths toward that goal. (Note: The final version of these rules is available on the ARB's Web site, http://www.arb.ca.gov)

Curbing diesel emissions, particularly from buses, is a priority aim for the ARB. A bus operates in densely populated areas, and, with repeated stops and starts, exposes many people to its fumes. Besides a high ranking as a public nuisance, diesel fumes pose a serious threat to public health. Particulate matter (PM) from any source, especially ultra-fine particles, can cause acute and chronic lung disease. In people who already have impaired respiratory or cardiovascular function, this irritation can precipitate episodes of serious illness or even death. The particulate matter in diesel fumes is soot, which has also been determined to be carcinogenic and is listed by the ARB as a toxic air contaminant. Diesel exhaust also contains oxides of nitrogen (NO_x) and volatile organic compounds, which react together in sunlight to form ground-level ozone. NO_x is also an air pollutant in its own right. Both ozone and NO_x can cause acute and chronic lung impairment.

The ARB's proposed Public Transit Bus Fleet Rule is intended to further reduce diesel emissions by encouraging bus fleet operators to purchase or lease low-emitting, alternative-fuel vehicles. An agency may choose one of two paths to compliance -- the diesel or the alternative-fuel path. Both paths have the same requirements for NO_x fleet average, PM retrofits, and the use of low-sulfur diesel fuel by the transit agencies. The two paths have different applicable emission standards and different dates by which 15 percent of the agencies' new bus purchases must be zero-emission buses (ZEBs).

Under the proposed rule, from the date of its adoption to 2015, at least 85 percent of the new bus purchases of the agencies that choose the alternative-fuel path must be low-emission, alternative-fuel buses. In addition, the diesel path requires a ZEB demonstration project. Table 1 on page 3 shows the requirements of the proposed rule and the schedule for their attainment. Emissions from a vehicle are expressed as grams per horsepower (brake horsepower) for each hour of operation.

In order to reduce NO_x emissions from urban buses, both paths would require transit agencies to meet and maintain the rule's NO_x fleet average standard. Most agencies are expected to do this by retiring pre-1988 buses and replacing them with new, cleaner buses. This requirement is expected to reduce NO_x emissions statewide by 2 tons per day in 2002. Most of this reduction, however, would be the result of normal fleet turnover and is not considered in the state's required determination of the rule's cost-effectiveness.

To reduce PM emissions, ARB-certified PM retrofit devices would be required for all existing diesel buses and buses up to model-year 2004. These retrofit devices are not applicable to alternative-fuel buses. The proposed rule would establish a phased schedule for completing the retrofits. Briefly, all 1990 and earlier buses must be retrofitted by January 1, 2003; 1991 through 1995 buses by January 1, 2005; and 1996 through 2003 buses by January 1, 2009. The retrofits are expected to reduce PM emissions by 300 lbs/day statewide in 2005 and 100 lbs/day in 2010.

For the PM retrofit devices to function efficiently and reliably, low-sulfur diesel fuel must be used. Therefore, the proposed rule would require that, effective July 1, 2002, any diesel fuel purchased and used by a transit agency must be low-sulfur.

After January 1, 2004, the new diesel buses purchased by transit agencies choosing the diesel path would have to meet proposed new emission standards more stringent than those for other diesel vehicles, including other buses. Engine manufacturers would be able to choose to meet this special standard by applying aftertreatment devices to engines that are certified to meet the 2004 emission standards for other diesel engines. The standards for model-year 2004-2006 diesel or dual-fuel urban bus engines would reduce NO_x statewide by 5 tons/day and PM by 50 lbs/day in 2010. In 2020, NO_x would be expected to be reduced by 6 tons/day and PM by 60 lbs/day.

Transit agencies with at least 200 urban buses in their active fleet would be required to have a minimum of 15 percent of new bus purchases or leases be ZEBs. Agencies choosing the diesel path would have to begin their purchases in 2008, those on the alternative-fuel path, in 2010. The requirement would sunset in 2015. A ZEB is defined as an urban bus that under all conditions of operation produces no emissions of the criteria pollutants or precursor pollutants. Included are battery-powered buses, hydrogen-powered fuel cell buses and electric trolley buses. This requirement is intended to provide long-term clean air benefits and to foster advances in alternative fuel technology. At least one manufacturer, Ballard Power Systems, expects to produce ZEBs commercially by 2002.

Transit agencies choosing the diesel path with at least 200 buses in their active fleets would be required to have 3 (or more) ZEBs in service by July 1, 2003 to meet the ZEB demonstration project requirement. Several transit agencies in an air basin could participate in a joint ZEB demonstration project.

In addition to the proposed Public Transit Bus Fleet Rule, the ARB proposes more stringent emission standards for 2007 and later model-year urban buses and engines that would tighten NO_x emissions. NO_x emissions are expected to be reduced by less than a ton statewide in 2010 and just over one ton in 2020. The EPA is expected to adopt similar 2007 standards.

Implementation of the proposed Public Transit Bus Fleet Rule would create significant costs for transportation planning agencies and the transit agencies. The requirements for the NO_x fleet average standard, PM retrofits, the use of low-sulfur diesel fuel, new bus purchases, and alternative-fuel bus purchases carry significant costs.

The ARB anticipates that federal, state, and local funds would be available for the new bus purchases necessary to meet the NO_x fleet average standard. Some transit agencies might not have sufficient funds to purchase new buses and might have to bear the cost of retrofits or repowering engines to meet the standard.

PM retrofits of buses would be phased in from 2002 through 2008. Each ARB-certified retrofit device is expected to cost about $3,000 installed. The ARB estimates that about 4,500 buses statewide will be retrofitted.

Low-sulfur diesel fuel is expected to cost about 5 cents more per gallon than ordinary diesel fuel.

An alternative-fuel bus is expected to cost about $40,000 more than a diesel bus. At least part of the excess cost may be offset by matching funds from FTA grants and incentive funding by state and local air quality districts. Operating costs for alternative-fuel buses vary, as reported by transit agencies that already have a significant number of these buses. Some agencies show cost savings.

The Carl Moyer Clean Engine Incentive Program is one source of funding that could be applied to the purchase of alternative-fuel buses, engines, or retrofits. Named for the late Carl Moyer, a clean-air technology scientist, the Program recognizes Dr. Moyer's contributions in this area and continues his efforts to improve air quality through incentives. Moyer Program grants may be applied to buses and trucks, off-road equipment including construction and agricultural equipment, marine vessels, locomotives, stationary agricultural equipment, and airport ground equipment. The Moyer Program is administered by the ARB and distributed by local air districts.

Moyer Program grants offset the higher cost of the alternative-fuel bus or engine over a diesel vehicle or engine. In some cases, cleaner diesel equipment may qualify for grants. The Program has distributed $44 million in the past two fiscal years, since July 1998; the ARB has asked that the funding for the Program be continued, as a cost-effective way to reduce air pollution.

The Bay Area Air Quality Management District also administers the Transportation Fund for Clean Air, generated by a $4 surtax on motor vehicle registration fees. Funds are awarded on a competitive basis to innovative or demonstration projects that reduce air pollution from transportation-related sources.

School buses were omitted from the proposed rule by the ARB because sufficient funds are not now available for them. However, prompted by the fact that children are more vulnerable than adults to toxic diesel fumes, the ARB has given a high priority to developing a rule to reduce school bus emissions. Meanwhile, the proposed Public Transit Bus Fleet Rule would set up an ambitious program to reduce diesel fumes from urban transit buses, mitigating the principal objectionable aspect of this sector of the state's transportation system.

Notes: Shaded area shows existing requirements and existing optional emission standards.

* Although transit agencies on the alternative-fuel path are not required to purchase engines certified to these optional standards, the staff expects that they will do so in order to qualify for incentive funding. At present, the only alternative-fuel engines available are certified to optional, lower-emission NOx standards. (Source: California ARB)